1. Field of the Invention
This invention relates in general to the field of structural noise suppression structures particularly adapted to use in aircraft jet engine housings and, more particularly but not by way of limitation, to an improved method and product for repairing sound suppression honeycomb sandwich panels.
2. Description of the Prior Art
In attenuating noise particularly associated with an aircraft jet engine a particularly efficient panel is the honeycomb noise attenuation structure disclosed in U.S. Pat. No. 4,291,079 dated Sep. 22, 1981. The sound attenuation structure shown in this patent has been found to be particularly effective in attenuating the specific broad range of frequencies customarily encountered in and around aircraft jet engines in various modes of operation of the aircraft. This sound attenuation structure comprises a honeycomb core having a usual multiplicity of endwise directed cells therein, a thin imperforate facing sheet bonded to one side of the honeycomb core, a perforated facing sheet having a multiplicity of perforations having a predetermined size and spacing bonded to the opposing side of the honeycomb core, and a thin sheet of woven metal cloth adhesively bonded to the outer exposed side of the perforated sheet. Typically, the honeycomb core and the imperforate facing sheet and the perforate sheet are made from aluminum alloys commonly used in aircraft applications.
The wire cloth is typically made from an aluminum alloy or from a stainless steel alloy. Such sound suppression panels are exposed to a severe environment where they encounter a high speed grazing air flow and are exposed to a wide range of temperatures. Since commercial jet aircraft are operated throughout the world these sound suppression panels also encounter ground conditions that are also severe and are further exposed to the further difficulties associated with the operation and maintenance of commercial jet aircraft.
The aluminum wire cloth due to the nature of aluminum has tended to deteriorate in use and require replacement in the field. Similarly, the stainless steel cloth, while longer lived than aluminum cloth, also requires replacement in the field since even though the stainless steel wire cloth is isolated from the underlying aluminum perforated sheet by an adhesive bonding medium the opportunity does arise in manufacture and use for a galvanic coupling to occur between the wire cloth and the perforated sheet thereby causing deterioration of the stainless steel wire cloth to aluminum perforate bond interface and to cause partial disbonding from the perforated sheet. The manufacture of such sound suppression panels typically involve the use of adhesives that require curing in autoclaves under elevated pressures and temperatures.
In the field, it has been difficult to achieve a lower cost satisfactory repair including the replacement of such wire cloth media for this type of sound suppression panel since such repair requires elevated temperature cure and vacuum bag processing to provide a repair comparable to original manufacturing conditions using the same materials. Thus, a need has arisen for a satisfactory lower cost method of repairing this type of sound suppression panels on aircraft in the field.